Three major areas of investigation are to be continued. 1. Comparison of the chemical structures of Actin I and Actin II which were previously described in these laboratories. Both cyanogen bromide and protease cleavage of the molecules are being carried out with subsequent 2 dimensional fingerprint analysis. 2. State of the two forms of actin with respect to the recently described actin-binding protein of platelets. 3. Further characterization of the Ca ions -binding protein in platelets isolated in this laboratory. BIBLIOGRAPHIC REFERENCES: Malik, M. and Stracher, A. Allosteric Behavior of Platelet Myosin, Arch. Biochem. Biophys., 178, 1977. R.C. Lucas, Michael Gallagher and A. Stracher, "Actin and Actin-Binding Protein in Platelets", Symp. on Contractile Systems in Non-Muscle Tissues, North Holland-Elsevier, in Press (Jan. 1977).